The present invention is generally directed to radio frequency identification (RFID). More specifically, the present invention is directed to using RFID to track a variable condition.
Radio frequency identification (RFID) is a term for technologies that use radio waves to automatically detect RFID tags. There are several methods of identification, but the most common is to store a serial number that identifies the tag, and perhaps other information, on a microchip that is attached to an antenna (the chip and the antenna together are called an RFID transponder or an RFID tag). The antenna enables the chip to transmit the identification information to an RFID reader. The RFID reader typically converts the radio waves reflected back from the RFID tag into digital information.
RFID automatic identification methods can be used for the tracking of assets in a supply chain. RFID tags each having a unique identification number are typically attached to or incorporated in an asset, such as equipment, products, personnel, etc. The identification number of an RFID tag has a static value that is used to identify the RFID tag. As the tagged assets move, RFID readers read the identification number of the RFID tags in order to track the location of the tagged assets. Typically, RFID readers are stationary and can read tags within a certain range, regardless of a direct line of sight between a reader and a tag. Since RFID offers the benefits of detection of assets in proximity to a reader, rather than a line of sight required by bar code technology, RFID technology is seen as a likely successor to bar code technology in asset tracking.
RFID tags can be passive or active. Passive tags do not require an internal power source, and are powered by an electrical current induced from the RF signal transmitted by an RFID reader. The lack of an internal power supply allows passive RFID tags to be small and inexpensive. Unlike passive RFID tags, active RFID tags have internal power sources which are used to power the tags. Active tags are typically more reliable than passive tags and can transmit at higher power levels than passive tags, allowing them to transmit longer distances.